Electrostatic and Gravitational Transport of Lunar Dust in the Airless Atmosphere of the Moon

Since its formation about 4.6 billion years ago, the surface of the moon has become covered with a thick layer of fine dust which has been preserved in a pristine, ultrahigh vacuum condition without any atmosphere-related changes of its physical properties and chemical compositions. The lunar surface has no atmosphere. Yet, Apollo and surveyor missions observed there is an atmospheric glow in the horizon and streamers of dust arising from the surface and scattering solar radiation during the sunrise. Apollo astronauts saw fountains of lunar dust rising hundreds of kilometers above the surface. The Apollo landing sites showed that the moon is virtually an ocean of electrostatically charged dust containing fractured glass-like particles with a high adhesive property. We present here an analysis of electrostatic charging by the photoemission and solar plasma electrons based on the current understanding of surface dust and the environmental conditions of the moon. The photon- particle interactions causing the particles to be positively charged during the day negatively charged during the night by solar wind including the effect of the earth´s magnetosphere. The cyclical charging and charge neutralization processes are briefly discussed in view of the observed electrostatic levitation of the dust. As the moon rotates on its axis, the dividing boundary line between the illuminated (sunlit) and the shaded (dark) regions, called the terminator, across which the charge polarity of dust layer and the intensity and the electric field change, also rotates. The reversal of direction of the electric field along the dividing line and the rotational motion cause dust trajectories to cross the terminator. Possible inhalation hazards of the toxic surface reactive dust with sharp edges in the nano- and micrometer size ranges are considered to be high in view of the increased lung deposition efficiency caused by the electrostatic image and space charge forces. A clear understanding of- - the lunar dust dynamics is needed for developing effective dust hazard mitigation for future robotic and human missions to the moon.